The present invention relates generally to internal combustion engines and, more particularly, to a system for the removal of hydrocarbons from engine exhaust gasses and a reduction of hydrocarbon deposits in the engine interior.
Internal combustion engines do not burn fuel very efficiently, and as a result produce exhaust gasses containing by-products of incomplete combustion, such as carbon monoxide, nitrous oxides, and a variety of hydrocarbons. Even diesel engines, which use a higher air-to-fuel ratio than do gasoline (Otto cycle) engines, produce excessive nitrous oxides along with carbon monoxide and some hydrocarbons. These combustion by-products are undesirable because they are both harmful to the environment and wasteful.
Carbon monoxide is a known greenhouse gas and is also toxic in large quantities, since it is preferentially absorbed over oxygen in red blood cells. Some nitrous oxides are also toxic, and contribute to acid rain. And among the plethora of hydrocarbons produced by inefficient combustion are carcinogenic benzpyrene and nitroaromates. Inefficient combustion is also wasteful insofar as the carbon monoxides, nitrous oxides, and hydrocarbons may yet be further oxidized to release potential chemical energy stored within.
One method of removing inefficient combustion by-products known in the art is to pass the exhaust stream through an afterburner to fully oxidize the by-products therein. While this technique is effective in removing the combustion by-products from the environment, it is inefficient in that afterburning is an endothermic process, actually taking more energy to perform and so further reducing the engine""s efficiency.
Another method of removing inefficient combustion by-products known in the art is by using a trap to remove the by-products form the exhaust stream prior to its emission into the environment. Traps are most effective in removing hydrocarbons (soot) from the exhaust stream, and less effective at removing carbon monoxide and/or nitrous oxides. Further, traps must frequently be purged of the entrapped hydrocarbons so as not to become choked and block the engine exhaust stream, thus increasing ram pressure and decreasing engine power and efficiency. Purging may be accomplished by physically removing and cleaning the trap or through the application of heat to the trap sufficient to oxidize the entrapped hydrocarbons. In either event, purging the trap is time and/or energy consuming.
Another method known in the art of removing inefficient combustion by-products from engine exhaust is by routing some of the engine exhaust back into the air intake, such that the partially oxidized combustion by-products may be completely oxidized by the engine. This is known as exhaust gas recycling. While this method is efficient in reducing the level of inefficient combustion by-products (especially nitrous oxides and carbon monoxide) ultimately emitted by the engine, the exhaust gasses must first be cooled before being reintroduced into the engine in order to control the combustion process. Cooling is accomplished by routing the hot exhaust gasses through a cooling chamber. During cooling, hydrocarbons in the exhaust gas stream tend to condense or otherwise accumulate in the cooling chamber, eventually clogging it and necessitating a purge procedure similar to the one described above for the trap.
There is therefore a need for a way of preventing the accumulation of hydrocarbon residue from accumulating in the cooling chamber of an exhaust gas recycling system. The present invention addresses this need.
The present invention relates to a method and apparatus for at least partially removing hydrocarbons from the exhaust stream of an internal combustion engine as or shortly after the exhaust gasses leave the exhaust manifold and prior to cooling the exhaust for recycling through the intake manifold. In a preferred embodiment, a filter is placed in the exhaust gas stream substantially adjacent the exhaust manifold, allowing the removal of hydrocarbon combustion by-products from the exhaust gasses at a point before the exhaust gasses can travel downstream of the exhaust manifold and deposit hydrocarbon residue within the exhaust gas recycling system (i.e., the exhaust gas transfer pipes or conduits and other exhaust gas processing devices). This is especially important in engine systems employing exhaust gas recirculation technology, since the exhaust gas recirculation conduits and exhaust gas recirculation cooler generally comprise a closed-loop system that requires expensive time and labor to clean or replace and is susceptible to clogging from residual hydrocarbon condensation and deposition from the cooling exhaust gasses circulating therethrough.
The filter may include a catalyst material to facilitate the removal of combustion by-products at the temperatures typical of engine exhaust gasses. Alternately, the filter may instead include means to heat the exhaust gasses passing therethrough sufficiently to ensure more efficient removal of the combustion by-products. Still alternately, the filter may feature a combination of both a catalyst and heating means. The filter removes hydrocarbons from the exhaust gasses as they leave the exhaust manifold, reducing the hydrocarbon levels in the exhaust gasses so as to slow or prevent buildup of hydrocarbon residue further downstream. The filter may operate to oxidize the hydrocarbons and other combustion by-products as the exhaust gasses pass therethrough, it may trap the hydrocarbons for periodic thermal purging in which the hydrocarbon build-up in the filter is bulk oxidized, or it may do both.
One object of the present invention is to provide an improved internal combustion engine exhaust system. Related objects and advantages of the present invention will be apparent from the following description.